After the third decade of life the human skeleton begins to lose bone. That is, bone mass decreases in relation to bone volume. Endosteal cortical and trabecular bone is lost from both the axial and the peripheral sites of the skeleton. Menopause and the associated estrogen deficiency will enhance bone loss in females. It has also been suspected that bone loss is familial, mainly because of the increased prevalence of osteoporosis in relatives, although there are no satisfactory scientific data to support a genetic control of bone loss. While age-related bone loss does not usually interfere with the normal function of the individual, occasionally it will produce considerable thinning of the cortical bone shell, causing bones to lose their integrity and fracture more readily. Decreases in the trabecular bone would result to vertebral compression of fractures and fractures of the femoral neck. This project investigates the epidemiological, genetic, cross-sectional, longitudinal and cross-cultural aspects of bone loss among participants of the BLSA, and among genetic isolates from Europe, Japan, Australasia, Central America and Africa.